Electrodeposition of metallic chromium



Patented Sept. 14, 1926.

UNITED'ZASTATES EIJ'I SUZUKI, OF TOKYO, JAPAN, ASSIGNOR -TO GENERALELEC'IBIO GOMPANYQA PATENT OFFICE.

CORPORATION OF NEW YORK.

EILECTRODEPOSITION on unranmc cnnoMIuM.

m} Drawing. Application 1118a July 31, 1925, Serial No. 47,370, and inJapan January 19, 1925.

This invention relates to improvements in the. electro-deposition ofmetallic chromium. Its primary object is to provide a process by meansof which metallic chromium may be deposited. electrolytically upon metalsurfaces in a more economical manner than heretofore.

A further object of the invention is to produce a chromium deposit whichshall be more'adherent, dense, and resistant to high temperatures thanthe coatings hitherto produced.

One of the disadvantages of present chromium plating baths consists inthe necessity of using metallic chromium itself as the anode. In view ofthe ditficulty of obtain- .ing chromium sheets or plates in a state ofsufiicient purity for use as anodes in such baths, it is necessary touse platinum in lieu thereof, which, of course, entails considerableoperating expense and great initial investment. Furthermore, even whenchromium anodes are used, the rate of consumption must be regulated withprecision if a proper deposition is desired.

In the present invention these disadvantages are obviated by making useof the fact that lead is relatively immune from attack by sulphuric acidbase or chlorine ions and accordingly lead is used as the anode incombination with a special bath whose characteristics will be pointedout below.

In the preferred embodiment of my invention an electrolyte is used whichcontains a mixture of chromic acid and chromium sulphate and othersuitable chromium salts such, for example, as chlorine compounds ofchromium as the principal constituents and carbolic acid, boric acid-orglycerine as the auxiliary or addition agent. With a solution of thecharacter described, the lead will precipitate owing to the presence ofthe sulphuric acid base or chlorine ions and it will therefore notinterfere with the operation of the bath. I

Using a lead anode and the addition agents herein mentioned, I havefound that the following bath gives satisfactory results although it isto be understood that the proportion of the ingredients used may varywithout departing from the scope of the invention as pointed out withparticularity in the appended claims:

Per cent.

.(lhromic acid 5 to'10 Chromium sulphate 5 to 15 Boric acid 5 Ashereinbefore stated, glycerine or carbolic acid mav be used in lieu ofthe boric acid as an addition agent.

It will be found that the metallic chromium deposited from the bathdescribed above will be dense, firmly adherent, and capable ofwithstanding exposure to high temperatures.

\Vhat I claim as new and desire to secure by Letters Patent of theUnited States, is 1.- A process for the electro-deposition of metallicchromium consisting in conducting an electrolyzing current through asolution containing chromic acid 5 to 10%, chromium sulphate 5 to 15%,boric acid 5% from a lead anode to the article to be coated as acathode. 2. A process for the electro-deposition of chromium whichcomprises supplying current from a lead anode through a solutioncontaining 5 to 10% chromic acid, 5 to 15% chromium sulphate andapproximately 5% of an addition agent to the article to be coated as acathode.

In witness whereof, I have hereunto set my hand this 9th day of July,1925.

EIJI SUZUKI.

